1. Field of the Invention
The present invention relates to a means of providing highly directional acoustic cues to mammals underwater and, more particularly, to a method of alerting marine mammals and other mammals underwater to the danger of approaching motor vessels by projecting highly directional pulsed acoustic signals underwater within a predetermined frequency range.
2. Description of the Related Art
The danger of being struck and run over by motor boats presents one of the greatest threats to mammals underwater. Unlike many fish and other sea life, mammals such as manatee, whales and even humans generally have limited perception and reaction abilities underwater, thereby making it difficult to detect the presence and directional movement of an approaching motor boat in sufficient time to take evasive action. It is therefore not surprising that one of the leading human related causes of death for the endangered manatee is collision with boats. The inability of manatees to avoid collisions with boats was a mystery until the inventors hereof embarked on a research program to study the sensory capabilities of the manatee. Therefore, the only prior method of avoiding manatee/boat collisions was to impose very restrictive speed limits on boats operating in manatee habitats.
It is generally known that fish react to certain acoustical signals underwater, and thus various systems and methods for controlling fish behavior have been developed in the related art. Some of these systems are designed to elicit attraction or repulsion behavioral responses in fish. Examples of these types of systems are disclosed in the Kowalewski, U.S. Pat. No. 4,646,276 and E. L. Pipkin et al, U.S. Pat. No. 3,538,493. Still other methods using sounds projected underwater are designed to modify fish behavior in a manner causing them to swim along a desired path, as disclosed in the Suomala, U.S. Pat. No. 4,932,007. While the various systems and methods in the related art have been found to be useful for their intended purpose, namely controlling fish behavior, they are not suitable for use to alert marine mammals and other mammals underwater of impending danger. Specifically, the fish behavior control systems known in the related art generally operate at frequency levels below one 1 kHz, which is too low to be audible to most mammals underwater in a near surface marine environment. Further, none of the systems known in the prior art are designed to project a highly directional pulsed acoustical signal underwater and in the direction of movement of a motor vessel, within a frequency range audible to mammals underwater and near the water surface so that mammals along the path of travel of the vessel will be alerted to the danger and thus be prompted to take early evasive action.